rebeccry
I'm looking to find a telescope that can be used for astrophotography. I have a Nikon D90 DSLR. I'm on a limited budget and I'm wondering what I need to get started. I am looking to get some telescope recommendations and it sounds like I'll need an equatorial mount and a tracker. Any suggestions are welcome. I'd like to do some deep sky images. If anyone can give me a list of what I'll need I would appreciate it.
Thanks,
Rebecca
Answer
This is going to be long, since astrophotography is several levels more complex than either using a telescope by itself or regular photography.
One of the easier ways to get started is with your camera only mounted on a tripod. This allows you to start with "star trail" astrophotography. Simply point the camera towards Polaris and leave the shutter open for a period of time. Granted, this is a pretty easy step, but it gets you into the basics.
http://www.astropix.com/HTML/I_ASTROP/TRIPOD/TRIPOD2.HTM
Next, you can build a simple platform called a "Barn Door Tracker" (also known as a "Scotch Mount")
At its simplest, it is nothing more than two pieces of wood that are hinged together that have a threaded screw and a ball socket for the camera. These are good for up to around five minutes worth of tracking.
http://www.nightskypix.com/equip/ScotchMount.htm
For your camera, you will need a little device called an intervalometer. This controls the camera's shutter time and number exposers without you touching the camera. something like this -
http://www.amazon.com/Satechi-Timer-Remote-Control-Nikon/dp/B001QSG4R8
For lenses, it is usually better to use prime lenses (non-zoom) and something that you can manually focus. You have zero need for flash, auto-focusing, or automatic exposer control. What I use are the older, but still very good 35mm film camera lenses. Mostly these have a Pentax screw mount (M42) which you purchase an adapter plate that goes between your camera and the lens.
http://cgi.ebay.com/m42-lens-Nikon-D90-D700-D3000-D300-infinity-adapter-/360200287361#ht_2295wt_1141
Now comes the tricky parts -
You need to focus the camera to infinity, but the infinity marker on most lenses is not true infinity. You can either figure this out for yourself (time consuming) or do a simple depth of focus adjustment. This is where you stop the camera down about two stops and bracket the infinity between the width of the depth of focus.
For ISO settings, stay within about 200 to 800. Anything higher and the imager chip (CCD or CMOS) will begin showing noise and amplifier glow.
http://www.darkerview.com/CCDProblems/ampglow.php
Exposer times of course are going to be different, depending on your target. But one great trick you can do to help improve you image quality is a process called "image stacking". This is where you take a bunch of short length exposers and then have a software program add them together. Programs that do this are -
http://deepskystacker.free.fr/english/index.html
http://www.astronomie.be/registax/
Finally, back to your original question about telescopes and astrophotography -
Its all about the mount that everything sits on. It needs to be steady, have tracking and sturdy. It can not have any shaking or wobbling, it should only move when you want it to move (you don't want the mount to start drooping while the shutter is open). the mount and tripod should handle at least twice the weight of the telescope, camera and anything else attached to it. Basically, you want mass, lots of mass.
A simple, but effective tracking mount -
http://www.astrotrac.com/
Finally, down to the telescope - The better way to go would be with a apochromatic refractor or wide field reflector. The refractor would be more expensive, but would give you better results.
A few examples -
http://www.telescope.com/control/telescope-optical-tubes
Like I said at the beginning, its a lot of stuff to go through, but with patience you can work your way through the whole process.
And one last link for someone I know who is very, very good at this sort of stuff -
http://www.stargazing.net/david/
This is going to be long, since astrophotography is several levels more complex than either using a telescope by itself or regular photography.
One of the easier ways to get started is with your camera only mounted on a tripod. This allows you to start with "star trail" astrophotography. Simply point the camera towards Polaris and leave the shutter open for a period of time. Granted, this is a pretty easy step, but it gets you into the basics.
http://www.astropix.com/HTML/I_ASTROP/TRIPOD/TRIPOD2.HTM
Next, you can build a simple platform called a "Barn Door Tracker" (also known as a "Scotch Mount")
At its simplest, it is nothing more than two pieces of wood that are hinged together that have a threaded screw and a ball socket for the camera. These are good for up to around five minutes worth of tracking.
http://www.nightskypix.com/equip/ScotchMount.htm
For your camera, you will need a little device called an intervalometer. This controls the camera's shutter time and number exposers without you touching the camera. something like this -
http://www.amazon.com/Satechi-Timer-Remote-Control-Nikon/dp/B001QSG4R8
For lenses, it is usually better to use prime lenses (non-zoom) and something that you can manually focus. You have zero need for flash, auto-focusing, or automatic exposer control. What I use are the older, but still very good 35mm film camera lenses. Mostly these have a Pentax screw mount (M42) which you purchase an adapter plate that goes between your camera and the lens.
http://cgi.ebay.com/m42-lens-Nikon-D90-D700-D3000-D300-infinity-adapter-/360200287361#ht_2295wt_1141
Now comes the tricky parts -
You need to focus the camera to infinity, but the infinity marker on most lenses is not true infinity. You can either figure this out for yourself (time consuming) or do a simple depth of focus adjustment. This is where you stop the camera down about two stops and bracket the infinity between the width of the depth of focus.
For ISO settings, stay within about 200 to 800. Anything higher and the imager chip (CCD or CMOS) will begin showing noise and amplifier glow.
http://www.darkerview.com/CCDProblems/ampglow.php
Exposer times of course are going to be different, depending on your target. But one great trick you can do to help improve you image quality is a process called "image stacking". This is where you take a bunch of short length exposers and then have a software program add them together. Programs that do this are -
http://deepskystacker.free.fr/english/index.html
http://www.astronomie.be/registax/
Finally, back to your original question about telescopes and astrophotography -
Its all about the mount that everything sits on. It needs to be steady, have tracking and sturdy. It can not have any shaking or wobbling, it should only move when you want it to move (you don't want the mount to start drooping while the shutter is open). the mount and tripod should handle at least twice the weight of the telescope, camera and anything else attached to it. Basically, you want mass, lots of mass.
A simple, but effective tracking mount -
http://www.astrotrac.com/
Finally, down to the telescope - The better way to go would be with a apochromatic refractor or wide field reflector. The refractor would be more expensive, but would give you better results.
A few examples -
http://www.telescope.com/control/telescope-optical-tubes
Like I said at the beginning, its a lot of stuff to go through, but with patience you can work your way through the whole process.
And one last link for someone I know who is very, very good at this sort of stuff -
http://www.stargazing.net/david/
What would be a great lens for astrophotography?
Chris
I have a D3100 and I want to get into basic astrophotography. I was wondering what a decent lens would be for doing such? Could I do it with the basic lens that comes with the camera? And, if anybody knows, how long of a shutter speed should I use? Without a motorized tripod I do realize that the stars will be blurred but should I use a 10 minute? 20 minute? 3 hour exposure? Please reply. Thanks!
Answer
Depends what you want to do in astrophotography, if you just want star-trails then a 50mm lens is OK for the wide view, if you want to 'get closer' then you need a telescope with a T ring mount for your Nikon, they are surprisingly cheap.
Attaching any DSLR to a Newtonian isn't strait forward, often they wont focus on infinity as the lens mount to sensor distance is too long. The cure is either to move the mirror up the telescope tube or to use a Barlow lens which often comes with the telescope
http://www.youtube.com/watch?v=cYTmsfpL0M4&feature=related
Exposure times will be long, there is the '600 rule', if you want to expose with no discernible star movement then you divide the focal length of your lens into 600 and the result is the shutter time in seconds for pin-point stars. As an example a 50mm lens is 600/50 = 12, so you can have a 12 second exposure and still have no noticeable star movement, a 150mm lens would be 600/150 = 4 seconds and so on.
This is a good tutorial for star trails
http://www.jamesvernacotola.com/Resources/How-To-Photograph-Star-Trails/12233655_V7cX4D
If you want to fill your image with a wide view of the Milky Way then you need to observe the 600 rule or to use a motorised mount, lots of shorter exposures stacked will be better than one long exposure, you will have to increase ISO to record anything with these shorter shutter times. By stacked I mean to use stacking software to align and and super impose the images and to get the most detail from all the images, a little like an auto composite, this can 'magically' get loads of detail, but you will need to experiment.
For all these a Dark Sky site in the middle of nowhere works best, it's very difficult to do well in the light polluted skies of a City.
Photographing the Moon is a lot easier as the Moon is brighter than you think, the usual exposure for the Moon is 1/125th of a second at f8 and an ISO of 100, pretty much the same as a terrestrial shot. To fill the frame with the Moon on a 35mm film sized sensor you need a 2600mm lens to get the half a degree field of view that the Moon covers. The Moon moves it's own diameter every 5 minutes (Lunar time).
Telescopes offer a cheap way to get these long lenses, my Sky-watcher 130 Newtonian is the equivalent of a 650mm f4 lens! For around £200 complete with motorised equatorial mount a couple of eyepieces and heavy tripod, a pretty good deal. Use the supplied 2X Barlow lens and you have a 1200mm f8. You can mount your camera directly to this motorised mount and get pin sharp long exposures with the wide field of view. All in all a pretty good investment.
Chris
Depends what you want to do in astrophotography, if you just want star-trails then a 50mm lens is OK for the wide view, if you want to 'get closer' then you need a telescope with a T ring mount for your Nikon, they are surprisingly cheap.
Attaching any DSLR to a Newtonian isn't strait forward, often they wont focus on infinity as the lens mount to sensor distance is too long. The cure is either to move the mirror up the telescope tube or to use a Barlow lens which often comes with the telescope
http://www.youtube.com/watch?v=cYTmsfpL0M4&feature=related
Exposure times will be long, there is the '600 rule', if you want to expose with no discernible star movement then you divide the focal length of your lens into 600 and the result is the shutter time in seconds for pin-point stars. As an example a 50mm lens is 600/50 = 12, so you can have a 12 second exposure and still have no noticeable star movement, a 150mm lens would be 600/150 = 4 seconds and so on.
This is a good tutorial for star trails
http://www.jamesvernacotola.com/Resources/How-To-Photograph-Star-Trails/12233655_V7cX4D
If you want to fill your image with a wide view of the Milky Way then you need to observe the 600 rule or to use a motorised mount, lots of shorter exposures stacked will be better than one long exposure, you will have to increase ISO to record anything with these shorter shutter times. By stacked I mean to use stacking software to align and and super impose the images and to get the most detail from all the images, a little like an auto composite, this can 'magically' get loads of detail, but you will need to experiment.
For all these a Dark Sky site in the middle of nowhere works best, it's very difficult to do well in the light polluted skies of a City.
Photographing the Moon is a lot easier as the Moon is brighter than you think, the usual exposure for the Moon is 1/125th of a second at f8 and an ISO of 100, pretty much the same as a terrestrial shot. To fill the frame with the Moon on a 35mm film sized sensor you need a 2600mm lens to get the half a degree field of view that the Moon covers. The Moon moves it's own diameter every 5 minutes (Lunar time).
Telescopes offer a cheap way to get these long lenses, my Sky-watcher 130 Newtonian is the equivalent of a 650mm f4 lens! For around £200 complete with motorised equatorial mount a couple of eyepieces and heavy tripod, a pretty good deal. Use the supplied 2X Barlow lens and you have a 1200mm f8. You can mount your camera directly to this motorised mount and get pin sharp long exposures with the wide field of view. All in all a pretty good investment.
Chris
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